Come August 21, skies will darken, the temperature will drop, and the United States will be captivated by a solar eclipse sweeping across the country.

It's inexpensive and easy to experience the thrill of the moon sliding in front of the sun, blocking out its rays. But if not done properly, people could find themselves with lasting injuries.

"There is no feeling to the retina," explains Dr. Kirk Packo, adding that people won't even realize the development of "tiny, pinpoint, dead-center burns in the retina" brought on by staring at the sun.

Packo, chairman of the department of ophthalmology at Rush University, says people commonly think they can avoid this with multiple pairs of UV-protective sunglasses piled up--this is a big mistake.

"You're staring at the sun, very comfortably, for a couple minutes during the eclipse, all the while still living through the damaging effect of the UV spectrum that sunglasses do not block," Packo says.

The only option for direct viewing: special eclipse shades. According to NASA, these glasses must be certified as meeting the ISO 12312-2 international standard.

Sarah Smail from the Adler Planetarium adds that when using these special shades, the sun's disk is the only light source that should be visible.

"If you're seeing any light come thorough anywhere else, then those glasses are no longer safer to use," she adds.

If you are in the eclipse's path of totality (the dark gray strip in this map) you will be able to look up at the sun without glasses when the eclipse reaches totality. Chicago, however, will only see approximately 87 percent coverage of the sun, so no one in the Windy City will have that opportunity.

If you don't want to get glasses--or forget to order them early enough--there are still ways to enjoy the eclipse.

Many will make pinhole projectors, which focus the sun's light through a small puncture, displaying the eclipse on another surface. You can build one inside a cardboard box with some duct tape and tin foil, or simply poke a hole in an opaque sheet of paper. Even letting the sunlight slip through your intertwined fingers can create the projection. With all of these methods, people look away from the sun, with the light coming over their shoulders and passing through the pinhole projector onto the ground or other surface below.

This will take away any temptation of looking at the sun, making it a great option for families with young children who may try to pull off the protective glasses.

Whatever your plan, it's important to have one because the eclipse's peak comes and goes in a matter of minutes-- you don't want to miss this spectacular sight.